“7.21”北京特大暴雨个例分析I:水汽条件分析

Analysis of a Torrential Rain Occurring in Beijing on 21 July 2012: Moisture Analysis

利用地面观测资料、NCEP再分析资料、FNL资料等,对2012年7月21~22日北京地区发生的一次特大暴雨过程中的大尺度环流背景场和水汽条件进行了分析。结果表明,此次降水过程可分为2个阶段,第1阶段为21日10：00~20：00,呈现对流性降水的特点,第2阶段为21日20：00~22日04：00,以锋面降水为主;此次特大暴雨过程的影响天气系统主要有500 h Pa低槽、低空低涡、地面倒槽、冷锋;7月21日北京全天整个对流层水汽含量充沛;水汽来源主要有2支：一支来自副高外围海上暖湿东南气流和南风气流的输送,一支来自西南低空急流水汽输送,其中后一支水汽输送在此次暴雨过程中起主要作用;北京地区低空有非常强烈的水汽辐合中心。

Using the ground observational data,NCEP data,FNL data,etc. the large scale circulation background and moisture condition of a torrential rain occurring in Beijing during July 21- 22,2012 was analyzed. The results showed that the precipitation process can be divided into two phases. The first stage was from 10： 00 to 20： 00 on July 21,in which the precipitation was mainly from the convective system. The second stage was from 20： 00 on July 21 to 04： 00 on July 22,in which the precipitation was mainly from the frontal system. The main systems influencing the precipitation process were trough at 500 h Pa,low vortex,the ground inverted trough,a cold front. On July 21,the whole troposphere in Beijing area had sufficient moisture. Moisture mainly came from water vapor transport by southeast flow and south flow outside the subtropical anticyclone and the southwest jet at low level which plays a major role in the whole process. Very strong vapor convergence center appeared in Beijing area.